Why muscle memory is (mostly) in your head
Genetic changes induced by exercise don't stick around too long in leg muscles – even after three months of training. Belinda Smith reports.
They say you never forget how to ride a bike. This idea is often attributed to “muscle memory”, where actions or a skill are somehow imprinted into muscle tissue which makes it easy to do again, even after a long time off.
A Swedish study published in the journal PLOS Genetics has put a dent in this belief.
Skeletal muscle is one of the most plastic tissues in the body. Anyone who’s lifted weights might have admired their muscles growing in response. But there’s more to exercise than packing in more muscle cells.
During exercise, different genes in the muscle cells are switched on and off. Exactly which change was largely unknown, as was if those molecular effects lasted long after a period of training was up.
So Malene Lindholm, Stefania Giacomello and colleagues enlisted 23 young, healthy, non-smoking volunteers to find out.
The posse of participants had biopsies taken from both quadriceps, the big muscle at the front of the thigh, then embarked on a 12-week leg strengthening regime of four sessions per week – but only exercised one, randomly selected leg the entire time.
After the final training session, quadricep biopsies were taken again. The researchers sequenced the genome of each sample and found more than 3,000 genes were dialled up or down in trained cells compared to their rested counterparts.
Nine months later, 12 of the subjects embarked on a second 12-week training period. This time, instead of training one leg, they trained both, with each leg subjected to four sessions a week.
Biopsies taken before and after this exercise block showed both leg muscles underwent huge genetic changes.
But when they compared the previously exercised leg to the previously rested leg, they found no molecular differences.
This suggests muscles don’t have a memory after all. If they did, the researchers would see a different genetic response in the previously exercised leg.
So why does the “muscle memory” myth abound – and why do some activities feel natural when revisiting them?
While skeletal muscle doesn’t seem to retain memory, your brain certainly does.
Learning and retaining motor skills relies heavily on the cerebellum, the bit of your brain that looks like a tiny brain tacked on underneath.
A certain type of nerve cell called the molecular layer interneuron controls electrical messages leaving the cerebellum and turns them into a signal that that be laid down as memory in other areas of the brain.
Memories, as we know, can last decades. Some motor control memories, it seems, are no different.
This is why an adult who’s not cycled since a teenager can keep upright on a bike without having to go through training wheels again.
But if you're planning to do this, maybe start on grass first – at least until your brain dredges up the necessary memories.